Preparation of free guanidine and biguanide bases



Nov. 9,v 1943.

J. T. 'rl-iuris'romA v PREPARATION OF FREE GUANIDINE ANDBIGUANIDE BASES Filed March 14, 1941 R54 c r/a/V Vessel.

F/z. rs?

.sr/PONG' COMPRESSOR INVENTOR. JACK T. THURSTON,

BYZQSMMMN ATTORNEY.

Patented Nov. 9, 1943 UNITEDJSTT v ritErAaATfioNoF FREEGUANmnNE-AND v 'i I :,1., U lcfpNmEl-SASES Jack T. Thurston, vCos Cob, Conn., as signor lto American Cyanamid C o a corporation of Maine mPanyNew YorkfN-.Y-l

Appucationivrarcn V14,1941,semaine.383,277 t 9c1a.inis.(C1.26o-54) This invention relates to 'the preparation of guanidine and bFJLIanide bases andmore particularlyV it relates to a method lof recoveringsubstantially pure guanidine or biguanide as the 'free base from its salts.

Because of the instability of thel free bases they which heretofore^ has presented several difficulties.

If the biguanide acid-sulfate, nfor example, is treated with a caustic 'alkaliin an aqueousmediurn, free biguanidebase` cannot berecovered because of its extreme solubility. Furthermore the baseV decomposes if left in aqueous solution or picks up Vcarbon dioxidefrom the atmosphere to form biguanide carbonate if allowedto stand for any length 'of time.v `Not only is it necessary,

therefore, to prepare fresh quantities'of the base Whenever needed in chemical operations using a highly ineflicient process as regards yieldof the free base, but the product so obtained is extremely unstable and its purity cannot be relied upon.v In

many chemical syntheses the purity of vintermediates used is of prime importancein the course 'of the reaction 'andfwover-all yields; thedecomposition of biguanide; for example,which is an important intermediate in theeld of textile assistants and dyes, -not `only detracts from Ithe 4amount of product available for a given reaction, but decomposition productsmay inA some cases hinder the -process by either decreasing the reaction rate or causing a shift so that undesired reaction products are obtained. .Its use therefore as an intermediate, particularly in the preparation of guanaminesiis dependentV to a considerable extent on the easeand degree of puritywith which the free base can be obtained. Y

According tothe presentinvention Ihave found that when a 'guanidineor biguanide salt, such as biguanide acid sulfate which is obtained from the condensation of dicyandiamide and ammonia or amine salts, is suspended 'in lsubstantially nonaqueous liquid ammonia (95% or vhighexgNI-I),

`drous which materiallydncreases the yield of and a strong basic substance added, the f reeybase is formed which soluble inl liquid ammonia, whereas the sulfate radical unites with the basic substanceto form asalt which isundissolvedand can be removed by ltration.

directly, ammonia is evaporated at once.

A further modification of the present invention is the preparation of free `bases in ysingle st ep The bguanide re-4 mains stable in the liquid ammonia medium over" a considerable period of time or if itis to be used processes from `their V"primary reactants, using liquidammonia as the inert medium in which -the reaction is carried out. Inlarge commercial operations Where biguanide or guanidine is pret pared and used directly this permits a great saving' as the intermediate step of isolating the bases in the form of salts is eliminated. The-crude reaction mixture resulting from the synthesistis suspendedain liquid ammonia and the-free base y'recovered-on adding -a strong inorganic alkali rwhereupon the alkali metal salt andother impurities precipitate out and areffiltered, and the liquid ammonia solution yields a highfgrade, substantially anhydrous stable product.

In carrying out the present invention any strong inorganic alkalrcapable of setting free the lbiguanideor guanidine and which also `forms acid salts substantially insoluble in liquid ammonia canbe employedfw 'Ihus for example caustic alkalies such as sodium or potassium hydroxide are effective as well as their alkoxides such as sodium methoxide o r potassium ethoxide. It is advantageous in some cases to use the free metals such as sodium or potassium'directly as by this procedure the reaction iskept substantially anhy product. Therefore the `term strong basic substance as used inthe specification and claims is intended to cover both the" alkali metal hydroxides or alkoxides and the `free alkali metals.

It` is an advantage that contamination of the free4 base with excess `alkali can be avoided by using a liquid ammoniainsoluble alkali. Thus,

anyamount over that Atheoretically required to` free the base from its salt remains undissolved and. is ltered off with the insoluble alkali metal salt. f While, therefore, it is possible to useY any of the strong alkalis in the process of thepresent invention, the liquid ammonia insoluble alkalis are preferred.

The liquid ammonia used in practicing my invention is preferably substantiallyi anhydrous liquefied ammonia, but amounts of water not exceeding about 5 donot appear to materially de- V45` crease theefciency ofoperation. k

T he invention is generally shown` in the accompanying new sheet and will be described in `greater detail in conjunction with the following specific .examples which arel given by way'of illustration and thel invention is not intended` to bellimited thereby:

`Ecmrrple I Biguanide acid sulfate was -`suspended in liquid ammonia and two equivalents of finely powdered guanidinajA mono.-` K v'phenyl biguanide,V diethyl biguanide, diamyl vsodium hydroxideA were added. The reaction mixture was stirred for about one and one-half hours whereupon sodium sulfate was precipitated and removed by iiltration. On evaporation 'of the ammonia solution a high `yield of' -pure guanidine Was obtained.

Example III bodiments, it is tobe understood that 1it is not to be limited thereto but is to be construed broadly and restricted solely by the scope of the appended claims. v

What I claim is: 1. A method of preparing a guanyl base included in the group consisting-.of guanidines and 1biguanizdes which comprises ydispersing a crude mixture containingfa compound having the menvftioned guanyl radical in substantially anhydrous liquid ammonia, adding suicient amounts of a vstrong basic substance chosen from the group To 400 parts cfliquidammonia containing'U-' Y -parts vof n-biguanyl morpholine hydrochloride,

which was prepared from dicyandiamide and `morpholinehydrochloride, wasladded 8.3 parts of sodium metal. .Themetal dissolvedin the `solvent without sodarrriderformation and immediately@ combined with the acid radical'tol forni Ysodium vchloride whichvwas removed by filtration.. On "evaporation of the liquid ammonia yfiltrate, 53 partsfor 8,6% .of the theoretical yield of morpholinobiguanide melting at 155l57 C.

was obtained.

f A, i, Example IV Y y To l24fparts of 1',1 -dimethylguanidinehydrochloride dissolved in 800 parts of liquid ammonia vwas added 23 parts ofsodium metal. After-stirring the mixture, substantiallypfree of scd'amide,

the sodiumfchloride ywas removed by ltration and the ammonia rwas allowed to evaporate.

lThe yield of free 1,`1dimethylguanidine was '12 parts or'83% of the theoretical.

It is vnot intended that the `presentinvention be Vlimited to theuse of acid sulfates orhydrochlorides as the salts from which the free bases `are jobtained, but any form of a biguanide or guanidine combined with vother radicals, or crude mixtures containing Vthese compounds can be4 used. Bestfresults'are obtained, howevenwhe'n these other" groups are substantially insolubie'in liquid ammonia` asin suchr cases-the'selective solubility effects "a simultaneous purification lalong with 'the preparation ofthe ree=base.

y The process employed in the/above examples can likewisebe used to prepare other substituted aliphatic and aromatic guanidines and biguanides' ,such as "tri'rnethyl guanidine, 'l'.iloutylf guanidina mono'-, *di, and triphenyl guanidine,

ditol'yl guanidine, mono, di, and triethanol and dimethylvv buguanide,

biguanide,l A1,5l diallyl` biguanide,l 1,1,5,5 tetramethyl biguam'de, 1,1,2 tr'imethyl biguanide, 1,2,3 triphenyl' bigu'anide,v andthe like.

`It should be noted that in the presentinvention the liquid ammonia is used purely asa solvent and shouldfnot `be confused with lcasesv where liquid ammoniaf'has been used rto set free weak organic bases from their salts. In the present case, if a 'salt oi such a strong base as'bigua'- consistingvof alkali metals, their hydroxides and .alkoxides, to ,convert the guanyl compound to itsfreeib'as'e land-.flltering oi the insoluble prodnots. Y

2, A method-ofrecovering a substantially pure guanyl base included in the group consisting of guanidines and biguanides from a crude mixture, `which .comprises dispersing the mixture containying a compound l'lavingftheV mentioned 'the 'gu'anyl base. radicalin lsu'bstantially,anhydrous liquid nide or guanidine is vtreated with liquid amvmonia alone in the absence of a strong inorganic base such as caustic alkali, 'no substantial amount of free vbiguanide or guanidine would be set free.

:While the4 inventionhas4 been shownanufdef scribed'with particular' reference to speciiic em-I 1 ammonia. 30

taining -at lea'st .195%

y,amm-loma, addingV sufficient amounts oi a strong y basic substance chosen from the group consisting of alkali metals, Vtheir hydroxides and 'alkoxides, tocchi/'crt lthe guanyl compound `to its vfree base,'filteri ng on the-.insoluble products and recovering .the guanyl base by evaporationjoi' n 3. A method of preparing airee guanyl'base .included in .the'group ,consisting kci guanidines and biguanides from a' Tgllanyl salt which `comprises dispersingthefsalt in substantially anhydrous liquidlammoniavadding `sufiicient amounts of a jstrong'basic substance chosen 'from 'the .groupl consisting cf alkali metals, `their .hy-

droxides and alkoxides, to convert the .guanyl salt to its V` free lbase .and filtering voil `the Iinsoluble products.

v4. A- method 'of recovering .a free guanyl base included inthe groupconsisting of guandines .and bi'guanidesvirorna .guanyl salt which `com,-

prises dispersing the -salt Ain substantially Zan;

hydrous liquid .arnmonia, adding .sufficient `amounts ofa caustic alkalito convert the-.guanyl sait to its free base, altering oath@ vinsoluble alkali saltwand recovering the guanyl base -by yevaporation ofammonia. I

`rnetliodfor recovering a free guanyl base included in the-groupaconsistingg of guanidines and biguanides .from a guanylsalt which .com-

prises,dispe`1sing..the ksalt `in .substantially an-v hydrous liquid ammonia, adding sufiicient -1v amounts yof fan alkaiimetal to 'combine with. the acid radical. of itl-ie 'guanyl sait, .filtering -oi the insolublev alkali lsalt 'and .recovering :the guanyl base by` evapor'ti'on ofv ammonia.

6. A method of preparing aifree guanylfbase included 1in the Vgroup consisting of .guanidines `and biguanides from a-,guany'lfsalt-.Which comprises dispersing the saltfinliquidamnioniacon- NH3, :adding ,sutflcient amounts of a caustic kalkali to ccnvertt'he lguamirl saltr to itsfr-ee base-andiiltering olthe insoluble alkali salt.' f

f 7. A methodof recoveringa-ree'guanyl-base included inthe group yccn'sistngo'f guanidin'es *and biguanides'irom a guanylsalt which com- 'prises dispersing thesalt in liquid ammonia containing fat least v595% NH3, `adding -suiicient VAamounts of 'an alkali' metal to lcombine -withithe acid radical of the'guanyl Isalt,iilteringalii the "insoluble alkali salt and lrecovering the fguanyl `lziaseby4 evaporation o-ainx'nonifa` l Y 8. A method yof producing free guanidine from a biguam'de salt which comprises dispersing the a guanidine salt which comprises dispersing the salt in liquid ammonia containing at least 95% salt in liquid ammonia containing at least 95% NH3, adding sucient amounts of a caustic alkali NH3, adding suicient amounts of a caustic alkali to convert the biguanide salt to its free base and to convert the guanidine salt to its free base and 5 ltering on the insoluble alkali salt. ltering `oif the insoluble alkalilsalt. l

9. A method of producing free biguanide from JACK T. THURSTON. 

